As configurations of a low noise amplifier with broadband input matching, there are a resistive termination configuration, a common gate configuration, a resistor feedback configuration, and an active feedback configuration. Among these, the active feedback configuration using a common drain circuit is advantageous in noise, band width, and area and easily benefits from process miniaturization, and thus there is a high possibility that it will be widely used in the future.
In the common drain feedback low noise amplifier, a common drain circuit as a feedback path is connected between an input and an output of the amplifier (for example, see WO/2008/142051 Pamphlet). Since the common drain circuit is connected to the input, a bandwidth of input matching gets narrowed by a parasitic capacitance (an input capacitance) caused by the common drain circuit. The common drain circuit also acts as a noise source.
However, in the conventional common drain feedback low noise amplifier, it is difficult to reduce the input capacitance and the noise.